John
I can tell you this much, its a lot of work and you have to be quite savvy. The closest I came to being a fulltime dealer was back in 1999. Shows were a good way to make income buying & selling cards, but Ebay was even better. Much harder back then though since cell phones were just that....phones.
Before I go any further, I should mention that I was a modern card dealer and I can't believe that I'm going to admit this, but I even sold Pokémon cards. Please forgive me! Give me a second to put that skeleton back in the closet.
It was a good time for selling modern cards since game-used cards had just started appearing, autographed cards in packs were taking off and rookie cards were a solid sale.
Buying & selling at shows was very enjoyable for me since I got to meet and make friends with many people. Some of those people are close friends to me now. Selling on Ebay was different as in, all business. Given the impersonal nature of the internet, no face to face, basically it was list it, sell it, mail it and on to the next sale. Only twice did an Ebay sale touch on a personal side and that was when I sold a card to Tom Pagnozzi's nephew & the second time when an older Japanese gentleman living in Japan reached out to me and bought a Roy White autograph card from me since he was a teammate of White's when they played together in Japan.
I ended up getting out of it a few years later. I had a fulltime job during those years, but was making more selling cards than working on the clock. Kinda funny looking back now because my boss would ask me if I wanted to work overtime on the weekends and I would tell him no thanks since I could make more money sitting at home selling on Ebay.
How the times have changed in just the last 20 years.
Jantz
P.S. Anyone want to buy any Pokémon cards? Lol